Self-assembled quantum dots in the Si–Ge–Sn system have attracted research attention as possibleuddirect band gap materials, compatible with Si-based technology, with potential applications inudoptoelectronics. In this work, the electronic structure near the G-point and the interband optical matrixudelements of strained Sn and SnGe quantum dots in a Si matrix are calculated using the eight-band k.pudmethod, and the competing L-valley conduction band states were found by the effective mass method.udThe strain distribution in the dots was found within the continuum mechanical model. The bulk bandstructureudparameters, required for the k.p or effective mass calculation for Sn were extracted by fittingudto the energy band structure calculated by the non-local empirical pseudopotential method (EPM). Theudcalculations show that the self-assembled Sn/Si dots, with sizes between 4 and 12 nm, have indirectudinterband transition energies (from the size-quantized valence band states at G to the conduction bandudstates at L) between 0.8 and 0.4 eV, and direct interband transitions between 2.5 and 2.0 eV, whichudagrees very well with experimental results. Similar good agreement with experiment was also found forudthe recently grown SnGe dots on Si substrate, covered by SiO2. However, neither of these is predicted toudbe direct band gap materials, in contrast to some earlier expectations.
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